A major function of eukaryotic cells is the process of exocytosis, whereby materials contained in membrane-bound vesicles are released from the cell. In humans one major exocytotic function is secretion. Some of the basic knowledge of the cellular and developmental processes of secretion may eventually be useful in the understanding and treatment of a wide range of diseases resulting from secretory disfunction. The ciliophoran Paramecium tetraurelia has large (5 Mum) exocytotic organelles, the trichocysts, whose function to the cell is dispensible, since many genetic mutations causing lesions in the trichocyst phenotype have been isolated. Morphological, genetic, physiological and biochemical analyses of these mutations have allowed an overall view of the trichocyst developmental pathway to be constructed. A better understanding of the exocytotic precesses in P, tetraurelia, and the developmental stages leading to exocytotic competence, should provide a better foundation of knowledge for the general understanding of secretion/exocytosis. Although the general process of trichocyst development is now known, details of the process at many stages are still lacking, mostly due to a lack of enough mutations in trichocyst development. The study proposed here seeks to do a series of mutageneses to isolate new mutations in the trichocyst phenotype. A series of detailed analyses of these new mutations, and others on hand but not yet analyzed, will then be done. Analysis will include light and electron microscopy, genetic crosses to known mutations, a standard trichocyst function test using microinjections, and survey 1-D and 2-D gel electrophoresis of trichocyst proteins. Detailed study of all these aspects of the trichocyst phenotype will give us a better picture of the assembly and development of the trichocyst and ancillary cytoplasmic components needed for trichocyst function. Additionally, this kind of information may eventually facilitate advances in the molecular analysis of trichocyst development. In no other "model system" of exocytosis can so many different analytical techniques be used, sometimes on the same cell. What is known so far indicates that trichocyst development and exocytosis is generally similar, or at least comparable, to exocytotic processes in other cells; thus, basic information from paramecia is applicable to other systems.